Red Devil

You just need to buy or make a pair of horns for this one, and go to town with some creative makeup. Find a red or black dress, and you're all set. (A pitchfork is nice for effect -- you're a devil, after all -- but you can get away with skipping it!)

'Day of the Dead' Skeleton

Granted, this requires some face-painting skills, but there are a ton of Day of the Dead makeup tutorials you can follow to get a really great look. Pair your spooktacular face with just about any dress, and add a big flower to your hair.